Industrial material separation processes, like for instance flotation processes, are multivariable and highly non-linear. They are therefore hard to control. Measurements made on the performance of the process furthermore often need the use of X-ray refractometry. X-ray refractometry equipment is highly expensive and therefore there is often a desire to keep the number of measurement points to a minimum, which makes the control process difficult to implement.
There do exist models of such processes that can be used in such control. One is for instance described by Aldo Cipriani and Carlos Munoz, in “A Dynamic Low-Cost Simulator for Grinding-Flotation Plants”, Low Cost Automation, page 267-272, Buenos Aires, Argentina, 1995, IFAC.
However, most such models seem to be directed towards trying to control the grade of the concentrate and/or the tailings to desired set-points. Most plants do therefore seem to operate in regions far from their optimal condition.
In the field of pulp and paper production there has recently been provided an interesting control method. This method, which is a real time optimization control method, is described in WO 03/107103, where a dynamic model of the production process is provided. The document describes that a dynamic model can be optimised. However it does not really mention in which way the model should be optimised. It does only mention that there are trade-offs between different controlled output variables and that weighting can be used as a compromise between different competing targets.
There is therefore a need for a more efficient material separation process.